The present invention relates to novel aromatic AB2 imide monomers with thermally reactive trialkylsiloxy and aryl fluoride moieties, which can be polymerized to form hyperbranched aromatic polyimides in the presence of a metal fluoride catalyst.
Aromatic polyimides (PIs) are well known, high-performance materials with widespread applications in the aerospace and electronics industries due to their excellent thermomechanical and dielectric properties. Recently, it was demonstrated that they could be useful as optical materials based on their optical anisotropy when cast in directions parallel (in-plane) and perpendicular (out-of-plane) to the film surface. However, when fully imidized, most aromatic PI's have limited solubility in common organic solvents because of their structural rigidity and high degree of crystallinity; thus restricting the choice in processing options. Numerous research efforts have focused on organo-soluble PIs from the modification of the structure without substantially decreasing rigidity of their backbone. Solubility is desired in order to allow processing polymers with preformed imide units and to avoid the problems associated with handling poly(amic acid) (PAA) precursors. In addition, homogeneous, post-polymer reactions of soluble aromatic polyimides would allow better control in the introduction of desirable functional groups.
A viable alternative to attaining solubility in aromatic PIs is to change the traditional, linear geometry of the macromolecules to three-dimensional, highly branched (dendritic) architecture. As a subset of dendritic polymers, hyperbranched polymers have several important advantages such as better solubility compared to their linear counterparts, and easier synthesis than their analogous dendrimers, which involve tedious multi-step synthesis. Large quantity of hyperbranched polymers can be easily produced from ABx (x≧2) monomers. There are few reports on synthesis of hyperbranched PIs, and their utilization.
Accordingly, it is an object of the present invention to provided a self-polymerizable AB2 monomer of the generic formula

where R1, R2 and R3 which may or may not be the same; preferably, R1=R2=R3=Methyl; R1=R2=methyl and R3=ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl, neopentyl. The resulting AB2 monomer can be polymerized with the aid of a fluoride salt, preferably cesium fluoride, in catalytic amount to afford high molecular, low viscosity hyperbranched ether-ketone-imide polymer having repeating units with trialkylsilyloxyphenyl endgroups:

There has been a great interest in polymer-clay nanocomposites since nanoclays can improve the polymer mechanical and thermal properties at low loadings. Recently, dendrimers and hyperbranched polymers, with their globular conformations and a large number of polar end groups per molecule, have shown to promote exfoliation of nanoclay. For example, hyperbranched aliphatic polyesters such as commercially available Boltorn resins (Perstorp, Sweden) have been commonly used to intercalate and exfoliate Closite NA (Na+MMT) in water successfully. However, these aliphatic hyperbranched polymers are not suitable for high temperature conditions that are frequently necessary in aerospace applications.
Therefore, another objective of the present invention is to provide hyperbranched aromatic polyimide-clay nanocomposites.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.